Early detection of disease is of utmost importance in improving the odds of successful treatment. However, once a patient presents with disease symptoms, often, the disease is somewhat advanced or established. In order to truly discover a potential problem at earlier stages, asymptomatic patients should be screened for early signs of disease.
Glaucoma and other ocular and optic nerve-related diseases are among diseases that could potentially be detected at an early stage. There exists in the art a variety of tests that are capable of detecting early onset of glaucoma and other diseases of the optic nervous system. However, these tests are not suited as a screening tool to be used for the asymptomatic, general population.
For example, U.S. Pat. No. 6,527,391 to Heijl et al. is drawn to a typical method and apparatus for performing a computerized visual field test for identifying visual deficits. Such visual field tests typically are performed in one region of the eye at a time. They require long testing times and are compromised when a subject fixates on the wrong portion of a display. The recording of overt responses is also problematic in certain populations, including the preverbal, the nonverbal, the elderly and those who might intentionally or inadvertently hide their deficits.
U.S. Pat. No. 5,539,482 to James et al. is drawn to a glaucoma test using a pattern electroretinogram of a subject. In operation, the visual stimulus signals used are grating patterns, in contrast to a signal applied to individual eye zones modulated with a different temporal frequency. The use of an electroretinogram such as that proposed by James et al. for a glaucoma or vision test leads to a number of problems. An electroretinogram is highly problematic as it requires the attachment of an electrode to the cornea or sclera of a subject, who must thus have the eye locally anesthetized (and for children must be sedated) for the test. This limits the use of such a test to healthy populations, and demands that the test be performed in sterile environments such as hospitals. Moreover, known variations between subjects may cause the absolute comparison of any electroretinogram component to an “expected response component,” as described by James et al., to be inaccurate or insufficiently sensitive. A still further problem is that the electroretinogram only identifies deficits in the retina, and not in all the various other regions of the visual tract, such as along the optic pathway or even in the brain.
U.S. Pat. No. 6,477,407 to Klistorner et al. is drawn to the use of a multifocal pattern visual evoked potential (mfVEP) for use in detecting visual field loss by comparing electrical brain activity acquired over two or more regions of the brain using very limited signal processing, e.g., the use of phase, frequency, and magnitude components, compared to each other and to corresponding display factors, are not disclosed.
The above-mentioned tests all require either lengthy testing times, local anesthetization of the eye (and for children must be sedated) or require for a patient to hold his/her eye still for the duration of testing. In addition, they produce results that are difficult to interpret. For these and other reasons, these prior art tests are not adapted for screening of non-symptomatic, healthy patients.
Pattern VEP is a well-known diagnostic aid in the detection of glaucoma and other optic nerve-related diseases. However, as practiced in the prior art, pattern VEP suffers from a lack of specificity, due to the fact that a distorted signal may be as a result a possible aberration on the lens of an otherwise healthy eye. The inability to distinguish between a healthy and diseased eye deems ordinary pattern VEP less than suitable as a screening device.
Additionally, prior VEP testing, to be effective requires skilled operators whose knowledge and experience may be required to interpret the results. This lessens the availability of such testing to large segments of the public because of the limited number of skilled operators and it may also introduce errors in the analysis because of the subjective nature of the tests.
Thus, there remains a need for an objective simplified, quick and non-intrusive screening test to detect early signs of ocular and optic nerve disease in asymptomatic patients.